Digital and Analog Recording Contrasted
In analog recording, sound is recorded by converting continuous variations in sound pressure into continuous variations in electrical voltage, using a microphone. This varying voltage is then converted into a varying pattern of magnetization on a tape, or, alternatively, into a pattern of light and dark areas on an optical-film soundtrack, or a groove of varying deviation on an LP.
Because the physical characteristics of analog recordings relate closely to the sound waveform, replaying them is a relatively simple matter. Variations in the recorded signal can be converted directly into variations in sound pressure using a suitable collection of transducers and amplifiers. The replay system, however, is unable to tell the difference between wanted signals and unwanted signals. Unwanted signals might be distortions, noise and other forms of interference introduced by the recording process. For example, a record player cannot distinguish between the stylus movement it experiences because of a scratch on a record (unwanted) and that caused by a loud transient in the music (wanted). Imperfections in the recording medium are reproduced as clicks, crackles and other noises.
Digital recording, on the other hand, converts the electrical waveform from a microphone into a series of binary numbers, each of which represents the amplitude of the signal at a unique point in time, recording these numbers in a coded form which allows the system to detect whether the replayed signal is correct or not. A reproducing device is then able to distinguish between the wanted and the unwanted signals introduced above, and is thus able to reject all but the wanted original information in most cases. Digital audio can be engineered to be more tolerant of a poor recording channel than analog audio. Distortions and imperfections in the storage or transmission process need not affect the sound quality of the signal provided that they remain within the design limits of the system and that timing and data errors are corrected.
Digital audio has made it possible for sound engineers to take advantage of developments in the computer industry, and this is particularly beneficial because the size of that industry results in mass production (and therefore cost savings) on a scale not possible for audio products alone. Today it is common for sound to be recorded, processed and edited on relatively low-cost desktop computer equipment, and this is a trend likely to continue.
Excerpt from Sound and Recording: Applications and Theory, 7th Edition by Francis Rumsey and Tim McCormick © 2014 Taylor & Francis Group. All Rights Reserved.
About the Authors
Francis Rumsey is Consultant Editor and Technical Writer for the Journal of the Audio Engineering Society, and runs his own consultancy company, Logophon Ltd. Until 2009 he was a Professor at the University of Surrey (UK), specialising in audio engineering and psychoacoustics. He is chair of the AES Technical Council, a Fellow of the AES, and a busy organist.
Tim McCormick is aformer Deputy Head of sound at the Royal Exchange Theatre in Manchester (UK), has extensive experience in design and manufacture of audio electronics, and has worked at Klark Teknik and with the RSC at Stratford (UK) where he plotted and operated the sound for many shows as well as designing and building audio equipment when the need arose. Also interested in medieval architecture, The Cathedrals, Abbeys and Priories of Wales was published on 2010.